Getting a dog as a puppy isn't a guarantee that it will get along with cats. The thing about puppies is that they like to play. If the puppy isn't getting enough play time and discipline from its family, it will seek out the cat as a playmate instead. Many cats, quite understandably, will retreat when confronted with a large boorish puppy. The puppy gives chase, because that's what bored puppies do. Eventually this ritual escalates and hardens into hunting behavior that can become nearly impossible to retrain.